This Letter demonstrates the transporting and focusing of laser-accelerated 14 MeV protons by permanent magnet miniature quadrupole lenses providing field gradients of up to 500 T/m. The approach is highly reproducible and predictable, leading to a focal spot of (286 x 173) microm full width at half maximum 50 cm behind the source. It decouples the relativistic laser-proton acceleration from the beam transport, paving the way to optimize both separately. The collimation and the subsequent energy selection obtained are perfectly applicable for upcoming high-energy, high-repetition rate laser systems.

In the overall design of an inertial fusion reactor driven by ion beams or lasers the target design plays a central role. The concept of central ignition is used to reduce the input energy of the driver as much as possible. In this respect, the range of the 3.5 MeV alpha particles at 1-20 keV released by the fusion reactions in D-T is crucial for estimating the driver parameters. Further, for the calculation of the pellet gain and the burn processes, the ranges of alpha particles at temperatures up to 200 keV and at densities up to 1000 g*cnf 3 must be accurately known. The 14.1 MeV neutrons produced during the D-T reaction can collide with the deuterium and tritium ions and produce suprathermal knock-on ions which then slow down in the background plasma. This effect must also be calculated, especially for reactor-size pellets for which the pellet pR is comparable to the neutron mean free path. The stopping power of low atomic fusion products and deuterium and tritium ions in D-T is calculated, using the dielectric function theory for the stopping power of electrons. The theory of the energy deposition of ions in fully ionized, quantum and classical, ideal and non-ideal dense plasmas is reviewed. The GORGON computer code is used for the numerical calculations. The results obtained are compared with the results of other authors and with their theoretical methods.

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This paper discusses the feasibility of employing heavy-ion cluster beams to generate thermal radiation that can be used to drive inertial fusion capsules. The low charge-to-mass ratio of a cluster may allow the driver beam to be focused to a very small spot size with a radius of the order of 100 μm, while the low energy per nucleon (of the order of 10 keV) may lead to a very short range of the driver particles in the converter material. This would result in high specific power deposition that may lead to a very high conversion efficiency. The problem of cluster stopping in cold matter, as well as in hot dense plasmas has been thoroughly investigated. The conversion efficiency of cluster ions using a low-density gold converter has also been calculated over a wide range of parameters including converter density, converter geometry, and specific power deposition. These calculations have been carried out using a one-dimensional hydrodynamic computer code that includes a multigroup radiation transport scheme [Ramis et al., Comput. Phys. Commun. 49, 475 (1988)]. The problem of symmetrization of this radiation field in a hohlraum with solid gold walls has also been thoroughly investigated using a three-dimensional view factor code. The characteristics of the radiation field obtained by this study are used as input to capsule implosion calculations that are done with a three-temperature radiation-hydrodynamic computer code MEDUSA-KAT [Tahir et al., J. Appl. Phys. 60, 898 (1986)]. A reactor-size capsule which contains 5 mg deuterium–tritium (DT) fuel is used in these calculations. The problem of using a fuel mixture with a substantially reduced tritium content has also been discussed.

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